Three-piece type optical lens

A three-piece type optical lens, along an optical axis in order from an object side, comprising:

• a first lens element with positive refractive power that is a meniscus aspherical lens having a convex surface on an object side thereof;
• a second lens element with negative refractive power that is a meniscus aspherical lens having a convex surface on an image side thereof;
• a third lens element with negative refractive power that is a M-shaped aspherical lens having a M-shaped object side and a M-shaped image side while a central surface of the optical axis thereof is a convex surface or a concave surface;
• an IR cut-off filter;
• and
• an image sensor;
• wherein the optical lens satisfies following conditions:
• 0.4f≦d<0.9f
• 0.3<|R1/R2|<0.6
• 2.8≦Fno<3.6
• 0.2<br/f<0.4
• 0.5<f1/f<1
• −10.0<f3/f<−2.0
• wherein f is an effective focal length of the optical lens;
• d is distance between an object side of the first lens element and an image side of the third lens element;
• R1 is a radius of curvature of the object side of the first lens element, R2 is a radius of curvature of the image side of the first lens element, Fno is a F number of the optical lens, br is a back focal length of the whole optical lens of the present invention, f1 is an effective focal length of the first lens element, f3 is an effective focal length of the third lens element.